1. Field of the Invention
The present invention relates to a light source unit including a light emitting wheel and a projector including the light source unit.
2. Description of the Related Art
In these days, data projectors are used in many cases as image projection apparatuses which project screens or video images of personal computers and further images based on image data stored in memory cards on to a screen. These projectors are such that light emitted from a light source is concentrated on a micromirror device called a DMD (Digital Micromirror Device) or a liquid crystal plate for display of a color image on the screen.
In projectors of the type described above, conventionally, projectors using a high-intensity discharge lamp as a light source have been the mainstream of projectors. In recent years, however, there have been made many developments and proposals on light source units which use as a light source, a solid-state light emitting device such as a light emitting diode, a laser diode or an organic DL.
In a case where a light emitting diode is used as a light source of a projector, an output of a single light emitting diode is weak and therefore, a plurality of light emitting diodes need to be used altogether at the same time to obtain a high output. In a case where a plurality of light emitting diodes are used to form a light source unit, however, due to an increase in the number of bright points of the light source unit, it becomes difficult to concentrate light emitted from the individual bright points to a single point by an optical system once it has been so emitted, leading to a problem that the utilization efficiency of light emitted from the individual light emitting diodes is reduced. In addition, since the value of Etendue is large, there is much light which is unnecessary or is not used, leading to a problem that the utilization efficiency of the light emitting diodes is reduced. Note that Etendue is a value which represents the spatial expansion of effective light as a product of area and solid angle and which is preserved in the optical system. Consequently, the fact that the value of Etendue of a light source unit is larger than the value of Etendue of a DMD means that the amount of light which becomes unnecessary light increases.
In order to solve these problems, as is described in Japanese Unexamined Patent Publication No. 2004-327361, there is a situation in which a plurality of light emitting diodes are disposed in proximity to an outer surface of a spherical housing which is hollow and whose inner surface is formed into a reflecting surface, fluorescent materials are disposed at a central point of the spherical housing, whereby light emitted from the light emitting diodes is used as excitation light which causes the fluorescent material to emit light for use.
In addition, as is described in Japanese Unexamined Patent Publication No. 2004-341105, there is a situation in which excitation light is shone from a rear surface of a fluorescent wheel which is made up of a circular substrate and fluorescent materials which are disposed on the circular substrate in a circumferential direction for emission of beams of light in the wavelength bands of red, green and blue, which are three primary colors of light, and light emitted from the fluorescent materials is caused to be emitted from a front surface side of the fluorescent wheel for use.
Further, as is described in Japanese Unexamined Patent Publication No. 2003-295319, there is a situation in which a high-output laser diode is used in a light source unit in place of light emitting diodes. In this light source unit, fluorescent materials are disposed within a paraboloidal reflector and a laser beam is shone on to the fluorescent materials via a collimator lens (a collimating lens) and a condenser lens, whereby light produced by luminescence of the fluorescent materials is converted into parallel light by the reflector for use.
Although a higher output of the laser diode than that of the light emitting diode can compensate for the insufficient output of the light emitting diode, since coherent light (light with complete phase relationships) is emitted, when laser light is emitted directly to the outside of the light source unit or a projector which includes the light source unit in the form of coherent light, there exists a danger in which the eyes of a human being are badly affected. In the related art in which the laser diode is used as the light source, although there is no risk of light emitted from the laser diode is emitted directly to the outside of the projector in such a state that the fluorescent materials are excited, in the event that the fluorescent materials are dislodged due to heat or deterioration with age, there has been a fear that light emitted from the laser diode is emitted directly to the outside of the projector. To solve this problem, there is an electrical control method in which a device is disposed in a light source unit for detecting the dislodgement of fluorescent materials, and when the dislodgement of the fluorescent materials is detected, the light emission of the light source is stopped immediately. In this electrical control described above, however, since there is caused a slight time lag, light emitted from the laser diode is allowed to be emitted directly to the outside of a projector for a minute period of time in reality. As described, since light emitted from the laser diode constitutes coherent light and its output is very high, should such laser light be emitted directly to the outside of the projector even for a minute period of time, a seriously dangerous thing will result therefrom.
In addition, in addition to the emission of laser light to the outside of the projector, in the event that high-output coherent light which is light emitted from the laser diode is shone on to various types of devices disposed within a housing of electric equipment, heat stays where the coherent light is so shone, which triggers a risk that the devices fail or a risk that adhesives are deteriorated with age.